1. Field of the Invention
The present invention refers to an overall communication method and system for vehicles, particularly automobiles, and which enables inside communication among the passengers of said vehicle at the same time it indistinctively permits any of the passengers to establish a call with the outside through a mobile telephone system integrated in the system itself.
Said inside communication among the passengers of a motorized vehicle is greatly obstructed by the presence of a high noise level in the interior of said vehicle, noise not only coming from the engine but also due to both the friction of the tires with the pavement and the wind. Furthermore, the location of the occupants is not usually the most suitable for maintaining a conversation since the passengers are not face to face, but rather people in the front part have their back turned to the occupants in the rear seats, and all this added to the distance between them, especially in those vehicles having three or more rows of seats, makes maintaining a conversation difficult. Likewise, the driver is occasionally obliged to take his eyes off the road in order to maintain a conversation and the passengers move or shift part of their body or members with regard to their seat positions, thereby altering the conditions of the acoustic environment inside the vehicle.
2. Background of the Invention
A problem occurring when installing a speech communication system, comprising microphones, amplifiers and speakers, in a closed area with limited volume and variable acoustic conditions (other variable noises also being present), such as the interior of an automated vehicle, the feedback phenomenon derivative occurs by adding sound signals emitted by the speakers and the environmental noise to the speech signals seized by the microphones close-by. To eliminate or limit the effects of such feedback, electronic circuits are used comprising digital filters associated to the amplifiers to filter the signal to be reproduced, greatly eliminating the echo effects.
Acoustic echo canceller systems applied to microphone and speaker assemblies are known in the state of the art, being possible to mention for this purpose patents EP-A-453293, EP-A-599450 and U.S. Pat. No. 5,245,665.
Patent application WO-A-98/56208 refers to a communication system especially designed for the cabin of an automated vehicle for the purpose of improving the clarity of spoken communication inside the closed area, comprising an echo canceller system for eliminating the feedback component.
Communication inside a vehicle implies an important challenge for acoustic echo control and for noise reduction. One or more microphones assembled in front of each passenger picks up the speech signal and, additionally, different noises from the engine, road or others. This signal is amplified and returned to the inside of the vehicle through the vehicle speaker system. This situation creates two main problems. First, as a consequence of the electro-acoustic coupling between the speakers and microphones, the entire system can become unstable with the bothersome effect of generating whistling. Secondly, as microphones pick up speech and noise, the overall noise level inside the automobile will increase. Therefore, an echo canceller system is necessary for preventing the system from electro-acoustically coupling and said system must also be capable of reducing the noise so as to prevent the noise level inside the vehicle from increasing or being reinforced.
In other words, said conditions pose some important demands for effective acoustic echo control and noise reduction. Acoustic echo control must prevent the entire system from electro-acoustically coupling and becoming unstable, with the additional problems that the system must enable always operating with two-way communication. Noise reduction must clean the signal of the microphone in order to prevent increasing or reinforcing the noise within the vehicle.
Acoustic echo cancellation is carried out by means of an adaptive digital filter or set of filters operating parallely with the microphone and speaker system in the interior of the vehicle. For proper functioning of said filter, the single presence of the echo signal is required, but, given the nature of the acoustic environment, the microphone seizes, in addition to said echo signal, the near-by speech signal and environmental noise, which can lead to a permanent interference of the adaptive filter. The acoustic echo is produced by the speech signal near the microphone, such that the echo canceller must always deal with the echo and with said near-by speech signal.
A known solution for this drawback proposes freezing the echo canceller carried out in the form of an adaptive digital filter, such as a FIR (Finite Impulse Response) filter whose coefficients are updated by using a standardized LMS (Least Mean Square) algorithm when conditions are detected that are susceptible to generating whistling due to coupling, according to that proposed in patent U.S. Pat. No. 5,706,344. However, due to the continuous changes in the conditions of the communication paths between the occupants and microphone-speaker assemblies, the system can become unstable and begin to generate whistling while the passengers are talking and/or gesticulating. Said latter patent also proposes adding a low level white noise in the form of a random signal suitable for identifying the communication path when there is no signal in the proximity of the microphone and aids filter stability. However, this low level white noise may bother passengers if they are next to the speakers, a condition which is practically unavoidable in the interior of a vehicle.
The system and method according to the invention make no use of any freezing of the acoustic echo canceller, nor does it use low level white noise.